linux-kernel - [PATCH v2 00/10] gpiolib: Handle immutable irq

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Message-Id: <20220405135444.199295-1-maz@kernel.org>
Date:   Tue,  5 Apr 2022 14:54:34 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Thierry Reding <thierry.reding@...il.com>,
        Joey Gouly <joey.gouly@....com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Hector Martin <marcan@...can.st>,
        Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Jeffrey Hugo <jeffrey.l.hugo@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Basavaraj Natikar <Basavaraj.Natikar@....com>,
        Shyam Sundar S K <Shyam-sundar.S-k@....com>,
        linux-gpio@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, kernel-team@...roid.com
Subject: [PATCH v2 00/10] gpiolib: Handle immutable irq_chip structures

This is a followup from [1].

I recently realised that the gpiolib play ugly tricks on the
unsuspecting irq_chip structures by patching the callbacks.

Not only this breaks when an irq_chip structure is made const (which
really should be the default case), but it also forces this structure
to be copied at nauseam for each instance of the GPIO block, which is
a waste of memory.

My current approach is to add a new irq_chip flag (IRQCHIP_IMMUTABLE)
which does what it says on the tin: don't you dare writing to them.
Gpiolib is further updated not to install its own callbacks, and it
becomes the responsibility of the driver to call into the gpiolib when
required. This is similar to what we do for other subsystems such as
PCI-MSI.

5 drivers are updated to this new model: M1, QC, Tegra, pl061 and AMD
(as I actively use them) keeping a single irq_chip structure, marking
it const, and exposing the new flag.

Nothing breaks, the volume of change is small, the memory usage goes
down and we have fewer callbacks that can be used as attack vectors.
What's not to love?

* From v1 [1]:
  - pl061 and AMD drivers converted
  - New helpers to keep the changes small
  - New warning for non-converted drivers
  - Documentation and TODO updates

[1] https://lore.kernel.org/r/20220223154405.54912-1-maz@kernel.org

Marc Zyngier (10):
  gpio: Don't fiddle with irqchips marked as immutable
  gpio: Expose the gpiochip_irq_re[ql]res helpers
  gpio: Add helpers to ease the transition towards immutable irq_chip
  gpio: tegra186: Make the irqchip immutable
  gpio: pl061: Make the irqchip immutable
  pinctrl: apple-gpio: Make the irqchip immutable
  pinctrl: msmgpio: Make the irqchip immutable
  pinctrl: amd: Make the irqchip immutable
  gpio: Update TODO to mention immutable irq_chip structures
  Documentation: Update the recommended pattern for GPIO irqchips

 Documentation/driver-api/gpio/driver.rst | 175 ++++++++++++++++++-----
 drivers/gpio/TODO                        |  19 +++
 drivers/gpio/gpio-pl061.c                |  32 +++--
 drivers/gpio/gpio-tegra186.c             |  32 +++--
 drivers/gpio/gpiolib.c                   |  13 +-
 drivers/pinctrl/pinctrl-amd.c            |  11 +-
 drivers/pinctrl/pinctrl-apple-gpio.c     |  29 ++--
 drivers/pinctrl/qcom/pinctrl-msm.c       |  53 ++++---
 include/linux/gpio/driver.h              |  16 +++
 include/linux/irq.h                      |   2 +
 kernel/irq/debugfs.c                     |   1 +
 11 files changed, 293 insertions(+), 90 deletions(-)

-- 
2.34.1